“Sunzi said: The good fighters of old first put themselves beyond the possibility of defeat, and then waited for an opportunity of defeating the enemy. To secure ourselves against defeat lies in our own hands, but the opportunity of defeating the enemy is provided by the enemy himself. Thus the good fighter is able to secure himself against defeat, but cannot make certain of defeating the enemy.”

As Military Adviser in China - Page 245 by Aleksandr Ivanovich Cherepanov - China - 1982.

It is unknown if Patton ever said these precise words. However, Anthony Cave Brown notes https://skeptics.stackexchange.com/questions/36062/did-gen-patton-say-we-defeated-the-wrong-enemy/36063#36063 in Bodyguard of Lies Volume II that "Patton was relieved of command of the 3rd Army by Eisenhower just after the end of the war for stating publicly that America had been fighting the wrong enemy— Germany instead of Russia", so it is at least an accurate paraphrase. For further discussion, see relevant threads on skeptics.stackexchange.com https://skeptics.stackexchange.com/questions/36062/did-gen-patton-say-we-defeated-the-wrong-enemy and /r/AskHistorians https://www.reddit.com/r/AskHistorians/comments/640pg5/what_did_general_george_s_patton_mean_when_he/.
Disputed

Address in Addis Ababa (5 May 1941), as translated in My Life and Ethiopia's Progress, Vol. 2, (1999), p. 165.
Context: Today is the day on which we defeated our enemy. Therefore, when we say let us rejoice with our hearts, let not our rejoicing be in any other way but in the spirit of Christ. Do not return evil for evil. Do not indulge in the atrocities which the enemy has been practicing in his usual way, even to the last.
Take care not to spoil the good name of Ethiopia by acts which are worthy of the enemy. We shall see that our enemies are disarmed and sent out the same way they came. As Saint George who killed the dragon is the Patron Saint of our army as well as of our allies, let us unite with our allies in everlasting friendship and amity in order to be able to stand against the godless and cruel dragon which has newly risen and which is oppressing mankind.

1950s, Loving Your Enemies (November 1957)
Context: Another way that you love your enemy is this: When the opportunity presents itself for you to defeat your enemy, that is the time which you must not do it. There will come a time, in many instances, when the person who hates you most, the person who has misused you most, the person who has gossiped about you most, the person who has spread false rumors about you most, there will come a time when you will have an opportunity to defeat that person. It might be in terms of a recommendation for a job; it might be in terms of helping that person to make some move in life. That’s the time you must not do it.

Source: Crocodile Tears

1950s, Loving Your Enemies (Christmas 1957)
Context: Third we must not seek to defeat or humiliate the enemy but to win his friendship and understanding. At times we are able to humiliate our worst enemy. Inevitably, his weak moments come and we are able to thrust in his side the spear of defeat. But this we must not do. Every word and deed must contribute to an understanding with the enemy and release those vast reservoirs of goodwill which have been blocked by impenetrable walls of hate.

Sergeant Richard Sharpe, p. 233
Sharpe (Novel Series), Sharpe's Triumph (1997)
Context: "Now we'll see how their infantry fight," Wellesley said savagely to Campbell, and Sharpe understood that this was the real testing point, for infantry was everything. The infantry was despised for it did not have the cavalry's glamour, nor the killing capacity of the gunners, but it was still the infantry that won battles. Defeat the enemy's infantry and the cavalry and gunners had nowhere to hide.

Source: Reflections on the Human Condition (1973), p. 127

Quoted by Granville Hicks in The Living Novel: A Symposium (Macmillan, 1957; digitized version in 2006), p. ix
General sources